Method of making formcoke



Jan. 15, 1963 E. GORIN ETAL METHOD OF MAKING FORMCOKE Filed Aug. 1. 1960NON-CONDENSABLE GAS S N M. OCONDENSABLE GAS N 8 E 0/ 7 w 8 CONDENSER m SS T M. EN.- 4 7 m s m m 7 H 0 2 m C 7 w m E O K N 8 O fi 5 CALC NER C 8o m 4 5 V F CONDENSER O 7 6 z m 5 O CALC NER v 4 L M R 2 R 4 M 0CONDENSER PM 4 F S w A w a 6 z w m G H 0M R N k E R E RM M L H L l 6 l Bm D M R E CARBON ZER M E n H k L m INVENTORS EVERETT GORIN ROBERT J.FRIEDRICH BY Lpfl fiwgz PITCH ATTORNEY 3,073,751 METHGD 6F MAKINGFORMCGKE Everett Gorin, Pittsburgh, and Robert J. Friedrich,Finleyville, Pa., assignors to Consolidation Coal Company, Pittsburgh,Pa., a corporation of Pennsylvania Filed Aug. l, 1960, Ser. No. 46,7% 7Claims. (Cl. 202-26) This invention relates to the production offormcoke from caking bituminous coals, and, more particularly, to theproduction of a formcoke which is suitable for use in conventional blastfurnaces.

The supply of caking coals particularly suitable for makingmetallurgical coke in conventional coke ovens is limited. it would behighly desirable to develop a method of making coke that would berelatively independent of the restrictive specifications imposed uponthe coals now employed in current coke plants. in particular, it wouldbe desirable to make coke from any caking bituminous coal which would beequal to or superior to that coke which is now made from very specialblends of coking coals. Such an accomplishment would extend the reservesof coal available for the metallurgical market.

This invention is primarily concerned with making coke from mixtures ofa caking bituminous coal and the solid distillation residue ofpreviously distilled coal, with or without the addition of pitch.Formulations of this general type have been used before in attempts tomake coke. These formulations have been transformed by briquettingpresses, by tumbling as in a rotary retort, or by other means intobriquets or agglomerates of predetermined sizes. The term formcoke hasbeen used to describe such products in a calcined state and is so usedherein. In general, the formcokes so far produced have been inferior toconventional coke with respect to their porosity, density or strength.In particular, their strength has not been adequate to sustain theburden of a conventional blast furnace, albeit adequate in someinstances for low shaft furnaces and the like. In the copendingapplication of Friedrich et al., Serial No. 635,277, filed January 22,1957, now abandoned, there is described a method of forming briquetsfrom a narrowly defined formulation of the general type mentioned above,and thereafter subjecting the briquets to a critical heating schedule inthe calcining step. While the resulting form'coke does have therequisite strength for blast furnace use, the rather precise heatingschedule imposes economic deterrents upon its commercial use.

Accordingly, it is the primary object of this invention to provide amethod of making agglomerates from a caking bituminous coal which, whencalcined by conventional means, will yield formcoke suitable for blastfurnace use.

Other objects of our invention will become apparent upon reference tothe following description and to the accompanying drawing in which apreferred embodiment of our invention is shown schematically.

in accordance with our invention, crushed caking biturninous coal andfinely divided char (is. the solid carbonaceous residue of coal whichhas been distilled between 800 and 1400 F.) are introduced into asubstantially horizontal rotary retort to fill at least ten percent byvolume of the retort, but preferably between thirty (30) and fifty (50)percent. If desired, pitch may be added at the same time to increase thedegree of fluidity of the coal upon being heated and to supply somebinder. The relative proportions of coal, char and pitch introduced intothe retort are: to 60 parts by weight of coal, to 65 parts by weight ofchar, and 0 to 15 parts by weight of pitch. The temperature within theretort is maintained in the range of 750 to 825 F. The desiredtemperature of the mixture in the retort is maintained under essentiallyadiabatic conditions, that is by 3,Zi,75l Patented Jan. 15, 1933 icepreheating the raw materials before admittance to the retort to supplyas sensible heat substantially all the heat required to achieve thedesired temperature in the tumbling zone. The retort is rotated toeffect tumbling and intimate mixing of the solids. As the mixture istumbled in the retort, discrete agglomerates are formed whileconcurrently partial distillation of the coal occurs, thereby evoivingtar, the pitch portion of which when recycled serves as an additionalbinder for the agglomerates when pitch is included in the formulation.The residence time of the solids in the retort is generally betweenfifteen and thirty minutes. The hot agglomerates are recovered from theretort and thereafter calcined at an elevated temperature, e.g. betweenabout 1500 and l800 F. During calcination no further agglomerate growthoccurs. in fact, the agglomerates produce formcoke of somewhat smallersize due to shrinkage during the calcination. The product forrncoke hasthe density, strength and abrasion resistance of conventional blastfurnace coke, and, in fact, the strength is generally superior to thatof conventional coke if made under the conditions set forth hereinafterin the description of the preferred embodiment of our invention.

However, before describing the preferred embodiment of our invention,those features and conditions of our process which are essential to theproduction of a formcoke suitable for use in a blast furnace will bedescribed. The success of our process is critically dependent upon themaintenance of narrowly defined conditions. Failure to observe theessential requirements set forth below results in no agglomerates atall, or in agglomerates too weak for blast furnace use, or in a singlemassive agglomerate.

The critical features of our process are as follows. The composition ofthe formulation must fall within the relative proportions of cakingcoal, char, and pitch set forth above. The coal must be a caking coal.However, it may be low volatile, medium volatile, or high volatile.Furthermore, the coal must not have been oxidized before use in ourprocess, and must not be exposed to xygen during the process. Ifoxidized coal is used, weak, friable formcoke is produced. The amount ofcoal must not exceed that specified, for otherwise large and weakagglomerates, or even a single solidified mass will be obtained. Thechar employed in the process may be derived from eithercaking ornon-caking coals including lignite and sub-bituminous coals by lowtemperature carbonization. Its cubic foot weight should be between 20and 35 pounds if a porous formcoke is desired. In such a case, the charshould be prepared from caking coal by a fluidized carbonizationprocess, whereby a very porous char is produced. The amount of char mustnot exceed that specified since either no agglomerates will be formed,or small weak pellets will be obtained. The pitch may be any pitch whichis free of constituents boiling below 400 C. and may be derived fromhigh or low temperature carbonization of coal. Excessive amounts ofpitch will have the same effect as too much caking coal.

The agglomerates must be formed in a tumbling zone, such as thatprovided by a rotary retort. To obtain the desired agglomerates, themixture of coal and char must occupy at least l0 percent of the volumeof the tumbling zone, and preferably between 35 and 50 percent. If theoccupancy is less than 10 percent only a small yield of agglomeratesunder the conditions of our process is obtained. Furthermore, the majorportion of the heat required, and preferably all, should be suppliedadiabatically in the form of sensible preheat of the components of theformulation. That is, the equilibrium temperature of the components uponmixing should approach that desired in the tumbling zone, preferably notmore than 25 F. below the desired zone temperature. If desired, somemixing may be effected before entry into the retort, but, if this isdone, care should be exercised to avoid reaching a temperature at whichagglomeration will prematurely occur; or if such temperature is reached,only a very short residence time should be allowed for the agglomeratesin the tumbling zone.

It is essential for the formation of strong formcoke, in accordance withour invention, to maintain a temperature in the tumbling zone which iswithin the range 750 to 825 F. If the temperature is below 750 F, thereis little or no a glomeration of the mixture. If the temperature isabove 825 F., carbonization of the agglomerates is too rapid, with theresult that the formcoke product is weak and friable. We have furtherfound that it is particularly important that the temperature of thetumbling zone must not approach the temperature of maximum fluidity ofthe cakiitg coal used in the formulation, but must be below that pointpreferably at least 25 F. lower than the temperature of maximumfluidity. Otherwise, agglomerates are formed which are too weak andfriable for blast furnace use. Still further we have found that thetemperature of the walls of the retort which enclose the tumbling zoneshould not exceed 825 F. because of the resulting too high carbonizationrate in the tumbling zone. Accordingly, only a very limited amount ofheat may be supplied to the zone through the walls, thus the necessityfor supplying the major portion of the heat adiabatically.

The resulting agglomerates, after being calcined, have properties quitesimilar to those of conventional blast furnace coke. Their stabilityfactor (as determined by the ASTM Method No. 13294-50) is at least 50and thus equal to that of the best blast furnace coke now in use.

Referring now to the drawing for a description of the preferredembodiment of our invention, finely divided caking bituminous coalhaving a size consist of, for example, 14 mesh x Tyler Standard screenis continuously fed through a conduit into a preheating zone 12 wherethe coal is heated by any conventional means to a temperature of about400 to 500 F. The stream of preheated coal is conducted through aconduit 14 to a low temperature carbonization zone 16. In this zone thecoal is heated to a temperature of about 900 to 1000 F., preferably in adense phase fluidized bed. The operation of such a carbonization zone isnow well known and does not form an essential part of this inventionexcept to the extent that the char so produced in a fluidized bed hasparticularly desirable properties when a formcoke of low density isdesired. Such char has a highly porous structure which is retainedthroughout the subsequent production of formcoke. The tar vapors evolvedfrom the carbonization zone are conducted through a conduit 18 to acondenser 20. Non-condensable gases are recovered through a conduit 22while tar condensate is recovered through a conduit 24. Hot char istransferred without intentional cooling through a conduit 26 to a rotaryretort 28. If desired, the char may be initially distributed the lengthof the retort by suitable means such as an elongated screw.

Non-oxidized coal in the proper relative proportion to the char issupplied to the rotary retort 28 through a conduit 30 from a coalpreheater 31. In contrast to the coal fed to the carbonizer 16, the coalin this case is preferred to be about A" x 0 size consist, that is,coarser than the coal fed to the carbonizer. It is preferably preheatedto a temperature between 500 and 650 F. However, the raw coal feed forthe entire integrated process may be screened into two fractions namely:4 x 14 mesh and 14 mesh x 0 (Tyler Standard screen). The 14 mesh x 0then becomes the feed to the carbonizer 16 while the coarser A x 14 meshfraction is fed to the preheater 31 and thence to the retort. We havefound that the formcoke of this invention is improved by the use of coalwhich is coarser than the char. Preferably the coal fed to the tumblingzone has a size consist between and 14 mesh Tyler Standard screen.

The tar from the aforementioned condenser 20 is fed through acontinuation of conduit 24 to a heated fractionator 32. The latterserves to separate the tar into a pitch fraction and a fraction boilingbelow 400 C. which is recovered through a conduit 34. The pitch iswithdrawn through a conduit 36. A portion of the withdrawn pitch istransferred through a conduit 38 to a preheater 43 and thence to therotary retort 23 into which it is introduced through suitable spraynozzles 42 near the inlet end of the retort. The pitch is preferablyheated to between 650 and 800 F. in the preheater 40.

The preferred proportions of char, coal and pitch fed to the rotatingretort are as follows: 45 to parts by weight of char, 40 to 55 parts byweight of coal, and 0 to 15 parts by weight of pitch. The preheattemperatures of these three ingredients are preferably 900 to 1100 F.for the char, 400 to 650 F. for the coal, and 650 to 750 F. for thepitch. However, the preheat temperatures are suitably adjusted inaccordance with the relative proportions of the three ingredients toyield an average temperature of the mixture of at least 725 F. but nothigher than 825 F. Additional heat, if required, may be provided byexternal heating of the retort walls provided the temperature thereof isnot allowed to exceed 825 F., or by internal heating as by a gas burner,to raise the temperature of the mixture in the retort to between 750 and825 F. The atmosphere in the retort should be non-oxidizing;consequently any air employed in any burner should be completelyconsumed.

The total feed to the rotating retort 28 is regulated so as to fill atleast 10 percent of the retort. However, sufficient free space must beafforded to permit intimate mixing of the ingredients upon rotation ofthe retort. A relatively deep bed of solids is thus maintained at alltimes in the retort. Such a deep bed is possible only because of the useof adiabatic heat in our process, since the use of externally suppliedheat would require a shallow bed to permit adequate heat transfer. It isimportant that a deep bed he maintained, for otherwise uniformly sizedcoherent agglomerates are not obtained under the conditions of ourprocess. The formation of the agglomerates is accompanied bydistillation of tar from the caking coal. Some of this tar as producedserves as a binder in the formation of the agglomerates. Accordingly,the amount of pitch fed to the retort is regulated in accordance withthe fluidity characteristics of the feed coal at the formationtemperature; the greater the fluidity the less extraneous pitch isneeded. The total feed to the rotating retort is also regulated toprovide a residence time in the retort of about 15 to 30 minutes.

The tar vapors evolved in retort 28 are removed through a conduit 44 toa condenser 46. The non-condensable gases are recovered from thecondenser 46 through a conduit 48. The tar condensate is withdrawnthrough a conduit 56 and transferred to the fractionator 32.

The hot raw agglomerates which, for the most part, range in size between/2 inch and 3 inches are removed from the retort 28 through a conduit52. The stream of agglomerates is preferably separated by screening (notshown) into two streams which contain the /2" x 1 /2" agglomerates andthe plus 1 /2 agglomerates, respectively. The purpose of this separationis to permit selection of optimum heating rates in the calciners. Thesmaller size agglomerates are carried through conduit 54 into the top ofa calcincr 56 while the larger size agglomerates are carried throughconduit 53 into the top of a calciner 64 Each of the calciners isadapted to operate under a pressure between 0 and pounds per square inchand at a temperature between about 1500 and 1800" F. A hot gas,preferably a reducing gas, is introduced into the bottoms of thecalciners through conduits 62 and 64, respectively. The hot gaszpassesupwardly and in countercurrent heat exchange relationship to thedownwardly moving stream of agglomerates. In calciner 56, the rate ofheating is regulated so as to be substantially higher than that providedin calciner 60, for example 30 to 40 F. per minute in contrast to to 20F. per minute in calciner 60. By such regulation the heating schedulebest designed to produce strong formcoke is provided. However, theprecise operation or the particular embodiment of such calciners is wellknown in the art and does not form an essential part of this invention.The purpose of the reducing gas is to lower the sulfur content of theproduct during the calcining step. The product forrncoke is withdrawnthrough conduits 65 and 68. Tar vapors and other gases are withdrawnfrom the top of the calciners through conduits 7t) and '72 into aconduit 74 which carries them to a condenser 76. The tar condensate isrecovered through a conduit 78, while the non-condensables are recoveredthrough conduit 80.

In the following Table l the pertinent data of a number of runs aretabulated which show the critical effect of temperature and compositionof the feed formulation.

on a 3" screen; and 29.9 percent of the product after removal of the31.2 percent was retained on a 2 screen, etc. The cumulative percentagesamount to 98.9, leaving 1.1 percent of solids less than /2 in size.

In the last column of Table I is reported the tumbler index of the plusl-inch fraction of each of the respective product forrncokes where suchindex was obtainable. The forrncoke was produced by calcining theagglomerates from the tumbling zone at 1800 F. Except where otherwiseindicated, this index was obtained as follows. One thousand grams of thecoke were tumbled in an eight-inch diameter drum fitted with three 1equally spaced lifting vanes which was rotated at 54 r.p.m. for 1080revolutions. At the conclusion of the test the weight percent offorrncoke equal to or larger than /2 inch was determined. This figure isreported as sumbler index and is a measure of the strength of theformcoke. Comparison of this index with the Micum index showed that thetwo are substantially the same. On the other hand the ASTM tumbler indexD294-29 is much lower since it is determined by a much more rigoroustumbling procedure.

T able I Formulation (weight percent) Temp. Product size (weight percenton) Run F. Tumbler index of No. tumbling +1 product Goal 1 Char Pitchzone 3" 2" 1 Oonven ionalkblast furnace 50 to 60 (ASTM) co e 1 3 50 I 500 800 1 7 32.6 42. 4 17.2 54 (ASTM) Conventionalkblast furnace 88 to 94.

co e 4.5 55 0 725 0 O 0 0 45 55 0 750 0 1. 5 4. 5 30 47. 5 47. 5 5 775 012. 5 67. 4 19. 3 95. 48. 0 42 10 775 34 20. 9 29. 9 13. 2 89. 60 0 8000 0 .5 10 55 0 800 O 20 33 22 89. 50 0 800 1. 7 32. 6 42. 4 17.2 95. 5.45 0 800 74. 7 17. 5 7. 7 95. 35 0 800 C'oked to solid mass e Maximumfiuidity60,000 DDPM at 830 1*. (determined by the Gieseler plast-ometerin accordanc with the published ASTM proposed procedure).

2 3 x 2 coke used for test. 3 Runs 1 and 8 are the same In these runs acaking bituminous coal from the Pittsburgh Seam was used. Its sizeconsist was A x 0 Tyler Standard screen. The char was obtained by thedistilla- They are included twice to facilitate comparison of ASTMtumbler index- In Table II, the pertinent data relative to the effect ofpercentage of retort volume occupied by solids are tabulated.

Table II Formulation (weight Solids 00- Product size (weight percent on)Tumbler index on product Run percent) Temp. cupancy sizes shown No. F.(percent of retort 01 Goal Char Pitch 3" 2 1" 3" 2 1" tion of a cakingbituminous coal, likewise from the Pittsburgh Seam. its size consist was8 x 0 mesh Tyler Standard screen. The pitch was a by-product oven pitchof 101 C. melting point obtained from the topping of high temperaturetar. The resulting mixture occupied about 40 percent of the retortvolume. The temperature of the final mixture in the rotating retort isgiven under the heading of Temp, F. The size distribution of the productfrom the rotating kiln is given under Product Size expressed as Wt.percent on the designated screen size. The percentages represent thepercent of total yield of solid product. The diiference between thetotal of the percentages listed and 100 percent is the amount of solidproduct below /2 inch in size. For example, in

According to the provisions of the patent statutes, we have explainedthe principle, preferred construction, and mode of operation of ourinvention and have illustrated and described what we now consider torepresent its best embodiment. However, we desire to have it understoodthat, within the scope of the appended claims, the in- ,vention may bepracticed otherwise than as specifically illustrated and described.

We claim:

The method of making formcoke which comprises establishing andmaintaining a tumbling zone in a retort, introducing finely dividedcaking bituminous coal and finely divided solid distillation residue ofcoal into said tumbling zone in the relative proportions of 35 to 60 byweight of said caking bituminous coal and 40 to 65 parts by weight ofsaid distillation residue, maintaining at least ten percent of thevolume of said retort filled with said coal and residue, maintaining thetemperature of said tumblin" zone between 750 and 825 F., supplyingsubstantially all the heat required to maintain. said temperature assensible heat of the materials fed to the retort, tumbling said coal andresidue in said tum bling zone under non-oxidative conditions untilagglomerates are formed, and thereafter calcining said agglomeratesat anelevated temperature, whereby particulate formcoke of great strength isproduced.

2. The method of making formcoke which comprises establishing andmaintaining a tumbling zone in a retort, introducing finely dividedcaking bituminous coal, finely divided solid distillation residue ofcoal, and pitch into said tumbling zone in the relative proportions of35 to 60 parts by weight of said caking bituminous coal, 40 to 65 partsby weight of said distillation residue, and up to parts by weight ofsaid pitch, maintaining at least ten percent of the volume of saidretort filled with said coal, residue and pitch, maintaining thetemperature of said tumbling zone between 750 and 825 F., supplyingsubstantially all the heat required to maintain said temperature assensible heat of the materials fed to the retort, tumbling said coal,residue and pitch in said tumbling zone under non-oxidative conditionsuntil agglomerates are formed, and thereafter calcining saidagglomerates at an elevated temperature, whereby particulate formcoke ofgreat strength is produced.

3. The method or" making formcoke which comprises establishing andmaintaining a tumbling zone in a retort, introducing finely dividedcaking bituminous coal and finely divided solid distillation residue ofcoal into said tumbling zone in the relative roportions of to 60 partsby weight of said bituminous coal and to 65 parts by weight of saiddistillation residue, said residue having been heated prior tointroduction into said tumbling zone to an elevated temperature suchthat upon admixture with said coal an average temperature of at least725 F. and not more than 825 F. is achieved, maintaining at least tenpercent of the volume of said retort filled with said coal and residue,maintaining the average temperature of the solids in the tumbling zonein the range of 750 to 825 F. and below the temperature of maximumfluidity of said coal, tumbling said coal and residue in said tumblingzone under non-Oxidative conditions until agglomerates are formed,withdrawing said agglomerates from said tumbling zone and thereaftercalcining said agglomerates at an elevated temperature wherebyparticulate formcoke or" great strength is produced.

4. The method of making formcoke which comprises establishing andmaintaining a tumbling zone in a retort, introducing finely dividedcaking bituminous coal, finely divided solid distillation residue ofpreviously distilled coal, and pitch into said tumbling zone in therelative proportions of 35 to parts by weight of said bituminous coal,40 to parts by weight of said distillation residue, and up to 15 partsby weight of said pitch, at least said residue having been heated priorto introduction into said tumbling zone to elevated temperatures suchthat upon admixture with said coal and pitch an average temperature ofat least 725 F. and not more than 825 F. is achieved, maintaining atleast ten percent of the volume of said retort filled with said threematerials, maintaining the temperature of the materials in the tumblingzone in the range of 750 to 825 F. and below the temperature of maximumfluidity of said bituminous coal, tumbling said materials in saidtumbling zone under non-oxidative conditions until agglomerates areformed, withdrawing said agglomerates from said tumbling zone, andthereafter calcining said agglomerates at an elevated temperature,

whereby particulate formcoke of great strength is produced.

5. The method of making formcoke which comprises establishing andmaintaining an agglomeration zone under nonxidative conditions within asubstantially horizontal rotary retort, introducing finely dividedcalzing bituminous coal and finely divided solid distillation residue ofcoal into said agglomeration zone in the relative proportions of 35 to60 parts by weight of said coal and 40 to 65 parts by weight of saiddistillation residue, maintaining ten percent of the volume of saidretort filled with solids, maintaining the temperature of the solids insaid agglomeration zone between 750 and 825 F., supplying substantiallyall the heat required to maintain said temperature by the sensible heatof said solids, rotating the retort to efiect intimate mixing of coaland distillation residue by virtue of the rotary motion of the retort,recovering agglomerated solids from said agglomeration zone andthereafter calcining said agglomerated solids at an elevatedtemperature, whereby particulate formcoke of great strength is produced.

6. The method of making formcoke which comprises establishing andmaintaining a tumbling zone in a retort, introducing into said tumblingzone the ingredients of a formulation consisting essentially of 40 to 55parts by weight of a finely divided caking bituminous coal, 45 to 55parts by weight of finely divided distillation residue of coal, and upto 15 parts by weight of pitch, maintaining between ten and fiftypercent of the volume of said retort filled with said ingredients,maintaining the temperature of said tumbling zone between 750 and 825 F.and below the point of maximum fluidity of said bituminous coal,supplying substantially all the heat required to maintain saidtemperature by the sensible heat of said ingredients, maintaining thetemperature of the walls of said retort below 825 F., tumbling saidingredients in said tumbling zone under non-oxidative conditions untilagglomerates are formed, and thereafter calcining said agglomerates atan elevated temperature, whereby particulate formcoke of great strengthis produced.

7. The method of making formcoke which comprises carbonizing finelydivided coal in a dense fluidized bed at a temperature between 900 and1000 F., separately recovering the products char and tar, fractionatingthe tar to recover a pitch fraction free of fractions boiling below 460C. introducing said char and pitch along with a finely divided cakingbituminous coal into a substantially horizontal rotary retort in therelative proportions of 40 to 55 parts by weight of coal, 45 to 55 partsby weight of char, and up to 15 parts by weight of pitch, said coal asfed being at a temperature between 400 and 650 F., said char between 900and 1100 F., and said pitch between 650 and 756 F., maintaining betweenten and fifty percent of the volume of said retort filled with saidcoal, chat and pitch, maintaining the temperature within said retortbetween 750 and 825 F. and below the point of maximum fluidity of saidbituminous coal, supplying substantially all the heat required tomaintain said temperature by the sensible heat of said coal, char andpitch, maintaining the temperature of the walls of said retort below 825F., tumbling said coal, char and pitch under non-oxidative conditions insaid rotary retort until agglomerates are formed, and thereaftercalcining said agglomerates at a temperature between 1500 and 1800 F.,and recovering particulate formcoke having a stability factor of atleast 50 (ASTM No. D294-50).

Aspegrcn Apr. 9, 1957 MattoX et al. Feb. 28, 1956

1. THE METHOD OF MAKING FORMCOKE WHICH COMPRISES ESTABLISHING ANDMAINTAINING A TUMBLING ZONE IN A RETORT, INTRODUCING FINELY DIVIDEDCAKING BITUMINOUS COAL AND FINELY DIVIDED SOLID DISTILLATION RESIDUE OFCOAL INTO SAID TUMBLING ZONE IN THE RELATIVE PROPORTIONS OF 35 TO 60PARTS BY WEIGHT OF SAID CAKING BITUMINOUS COAL AND 40 TO 65 PARTS BYWEIGHT OF SAID DISTILLATION RESIDUE, MAINTAINING AT LEAST TEN PERCENT OFTHE VOLUME OF SAID RETORT FILLED WITH SAID COAL AND RESIDUE, MAINTAININGTHE TEMPERATURE OF SAID TUMBLING ZONE BETWEEN 750 AND 825* F., SUPPLYINGSUBSTANTIALLY ALL THE HEAT REQUIRED TO MAINTAIN SAID TEMPERATURE ASSENSIBLE HEAT OF THE MATERIALS FED TO THE RETORT, TUMBLING SAID COAL ANDRESIDUE IN SAID TUMBLING ZONE UNDER NON-OXIDATIVE CONDITIONS UNTILAGGLOMERATES ARE FORMED, AND THEREAFTER CALCINING SAID AGGLOMERATES ATAN ELEVATED TEMPERATURE, WHEREBY PARTICULATE FORMCOKE OF GREAT STRENGTHIS PRODUCED.